Conventionally, in an image forming apparatus such as a copying machine, a printer, and a facsimile machine, a driving force transmission apparatus executing an intermittent rotation operation has been used as an abutting and separating mechanism for a transfer roller and as a sheet pick-up mechanism for a sheet feed unit, for example. Such a driving force transmission apparatus generally uses, for example, an electromagnetic clutch and a dedicated motor, to execute an intermittent rotation operation. However, since use of such an electromagnetic clutch and a dedicated motor results in a cost increase, Japanese Patent Application Laid-Open No. 3-158328 discusses a configuration that can be made at a lower cost.
FIGS. 13A and 13B schematically illustrate a configuration of a conventional driving force transmission apparatus discussed in Japanese Patent Application Laid-Open No. 3-158328. This configuration will be described below.
The driving force transmission apparatus includes a driving gear (driving member) 22 rotated in the direction of arrow A by a driving source (not illustrated) and a driven gear (driven member) 23 rotatable concentrically with the driving gear 22. The driven gear 23 holds a driving force transmission member 24 rotatable with respect to the driven gear 23 and movable between a position where the driving force transmission member 24 is engaged with the driving gear 22 and a position where the driving force transmission member 24 is disengaged from the driving gear 22.
As illustrated in FIG. 13A, when an engaging portion 24a of the driving force transmission member 24 is engaged with the driving gear 22, driving force is transmitted from the driving gear 22 to the driven gear 23 via the transmission member 24. As a result, the driven gear 23 and the driving force transmission member 24 are rotated in the direction of arrow A integrally with the driving gear 22.
To stop transmission of the driving force to the driven gear 23, as illustrated in FIG. 13B, an abutting member 17 is moved to a position where the abutting member 17 comes into contact with and locks the driving force transmission member 24. Accordingly, the driving force transmission member 24 and the driving gear 22 are disengaged from each other. In this way, transmission of the driving force from the driving gear 22 to the driven gear 23 is stopped.
According to Japanese Patent Application Laid-Open No. 3-158328, the driving force transmission member 24 is biased by a spring 25 so that the engaging portion 24a of the driving force transmission member 24 engages with the driving gear 22 without fail. Thus, to stop transmission of the driving force to the driven gear 23, the abutting member 17 needs to disengage the driving force transmission member 24 from the driving gear 22. More specifically, when the abutting member 17 comes into contact with the driving force transmission member 24, the abutting member 17 needs to separate (retract) the driving force transmission member 24 from the driving gear 22 against the force of the spring 25.